Portable devices (smartphones, tablet computers, personal digital assistants, and the like), which have lately become widespread, generally use a secondary battery as an energy source.
Such portable devices are each equipped with an input sensor configured to detect a change in electrostatic capacitance. When a conductor, for example, the user's finger or the like, comes close to the surface of a display panel of the portable device, the input sensor detects position information about the finger as operation input.
As the input sensor, there are an in-cell type sensor incorporated in a display panel and on-cell type sensor arranged on a surface of a display panel.
Besides, the portable device has a wakeup function. If the input sensor detects a conductor such as a finger of the user, the wakeup function brings, when the device is in the sleep state, the internal power supply circuit to the regular operating state, and shifts the display panel to the display state.
However, when the input sensor detects a conductor such as the finger of the user, the user does not always intend to use the portable device. There are many instances where the user only touches the portable device. For example, there is a case where the user simply stows the portable device in a bag, a case where the user simply switches the portable device from one hand to the other, a case where the user simply touches the portable device in the pocket, and the like. Besides, there is also a case where the portable device is frequently used by the user actually.
As described above, there are many instances where the energy of the secondary battery of the portable device is consumed. For this reason, under current circumstances, portable devices require charging of the secondary battery almost every day, and users find it troublesome.